Method of preparing fructose



Patented Feb. 1, 1927.

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No Drawing. Original application filed July 12, 18%, Serial No. 484,153. Divided and this application filed August 14, 1924. Serial No. 731,967.

This invention relates to an improved method of preparing fructose from inulin and the like and to the improved fructose product resulting therefrom.

The method of the present invention is applicable to inulin-containing materials of any kind but preferably it is applied to claritied and purified inulin solutions obtained from the ]1llCB of the dahlia bulb in accordance with the methods described in m copending applications, Serial No. 369,53 and Serial No. 424,459. When m improved method, particularly in its pre erred form, is applied to pure inulin, prepared according to these processes, the final fructose sugar product obtained is of unusual purity and is especially suitable for consumption as a food and alsopossesses unusually good keeping qualities. Q

Many attempts have hitherto been made to prepare a low cost sugar in the form of syrup, crystals, powder or the like, which could be substituted for sucrose (i. e. beet or cane sugar) for certain important uses such as the preparation of soda syrups and soft drinks, the preservation of fruits, the 'manu-.

facture of confectionery, for general cooking purposes, for table use and similar purposes. But these attempts have been at most only partially successful. The non-sucrose syrups prepared hitherto for commercial con sumption, such as starch syrups, corn syrups, malt syrups and the like, and all. the solid, powdered and partially crystalline products prepared from similar sources, have failed to meet the requirements which a sugar must have in order to complete in the market with cane and beet sugar products for many important commercial purposes.

Thus, for example, none of the foregoing .non-sucrose or sucrose substitutes rups are even approximately as sweet as t e syrups prepared from cane or beet sugar. Also such syrups are usually highly colored, and, therefore, cannot be used for many purposes for which ordinary refined cane or beet sugar syrup is employed and furthermore, certain.

of these syrups possess peculiar or variable flavors which render them undesirable for many of the purposes mentioned. Thus in the preparation of carbonated or soft drinks it is desirable that the syrup used shall have a definite and uniform flavor. If the stock readily handled.

syrup or sugar from which; the sodarap is prepared has a peculiar or variable ever as of its own, it is not possible to prepare from it (by adding a natural or artificial flavoring substance) a soda syrup having a flavor or taste of the desired definiteness or purity and uniformity. On the contrary in such in- W stances the finished soda-syrup will have a mixed flavor and this will vary with the varymg flavor of the stock syrup with which. the natural or artificial flavoring material or extract is mixed to produce the finished sodasyrup.

Likewise in the production of confectipm cry and culinary products uniformity and purity of flavor of the finished roduct is one of the "most important requirements and therefore the sugar or syrup used must not possess a variable flavor and preferably should not have a highly pronounced flavor of its own.

Furthermore, uniformity of color of all of the abovementioned finished products is an important additional requirement and for this reason stock syrups or sugars with a pronounced or non-uniform'- or objectionable color of their own are not suitable for these very important commercial uses.

The various solid, powdered, and partially crystalline commercial forms of the non-sucrose products hitherto produced to not meet the foregoing requirements and in addition most of them have also the undesirable property of absorbing moisture and becoming more or less past so that they cannot be lllany of them also undergo objectionable decompositions, when an attempt is made to keep them in storage for any considerable length of time or when they are employed in cooking operations or in the manufacture ofconfectionery.

The product of the present invention fulfills all the' foregoing requirements to an extraordinary degree and does not possess any of the above mentioned objectionable qualities and particularly it possesses the property of sweetness in much greaterdegrce than even cane 0r beet sugar. It is almost, if not quite, as free from objectionable colored impurities as is ordinary refined cane sugar syrup, so that it may be employed for all the purposes for which or inary water-white cane sugar. syrup is employed. Furthermore in syrup form' it may be cooked or.boiled without discoloration. Also in syrup form or in crystalline or solid form the fructosers'ugar food-product of the present invention is, resistant toward the attack of certain objectionable molds and bacteria and therefore possesses ood keepi g qualities.

Because of the ready availability and cheapness of the raw materials used and the simplicity and economy of the method by means of which the finished product of the present invention is produced, it can be manufactured at a very low cost.

The methods hitherto commonly employed for preparing pure fructose from inulin involve complicated and expensive methods of re-crystallization, usually from alcohol. Such recrystallization or other purification is made necessary because the older methods of hydrolysis yield discolored products or products which contain hygroscopic, deleterious or otherwise objectionable impurities and which are therefore unsuited for many of the uses for whichordi nary refined cane sugar products are emplciyed. This is true even when highly purifie inulin is used.

These impurities are very difficult to remove from the fructose by bleaching treatments, crystallization or similar methods and therefore to obtain the fructose in even an approximately pure form by these older' methods. it has been necessary to repeat the purification treatments a good many times. The final yield of fructose so obtained is, therefore, so small that the cost of manufacturing bythese older methods upon a commercial scale would-be prohibitive.

The method of hydrolysis employed in producing the product of the present invention produces fructose of a high degree of purity directly from the inulin and thus avoids all the foregoing difficulties and disadvantages. It is based mainly upon a regulated hydrolysis of the inulin under definitely controlled conditions and in its preferred form the hydrolysis is carried outwith a selected acid and also with a definite range of concentration of the acid. One of the most impprtant features of the improved method referred to is the adjustment of the time of hydrolysis to varying concentrations ofacid and to thevarying chemical nature of the acid. found that highly advantageous results are obtained by stopping the hydrolysis at the end of a. definitely determined period of time. in determining this correct time of hydrolysis, account is taken, as already mentioned, not only of the chemical nature of the acidbut also of the concentration of the acid and also in cetrair. instances of the temperature and pressure. By conducting the hydrolysis in this manner the inulin 'ient. property of fructose,

It has been is readilyhydrolyz'ed completely into fructose of a very high degree of purity and a solution of pure fructose is obtained directly from the inulin solution without the and thus the cost of evaporating the solution is entirely avoided.

In other methods sometimes employed; in the hydrolysis of inulin, a great deal'of uncertainty has existed as to the optimum duration of the hydrolysis in order to obtain best yields of fructose. These uncertainties in the older methods referred to'are due in large part to the circumstance that 'the intermediate hydrolyt-ic products of inulin, as well as the decomposition products, resulting from various-side reactions,all have properties which resemble those of fructose. If, therefore, one selects any convenand attempts to to determine the concentration of the fructose in the mixed solution by. measurements of this property, the results obtained will represent the resultant value of this property for all ofthe substances present. Thus, for example, since many of the hydrolytic and decomposition products are optically active or possess the power to rotate the plane of polarized light, the measurement -of'this property, as the hydrolysis progresses, does not always give a true measure of the concentration of fructose in the solution but corresponds to the resultant rotation of the mixture of all the optically active substances present. The measurement of the reducing power of the solution, as a. means of following the progress of hydrolysis, leads to similar confusing results for a similar reason, namely, that the various hydrolytic and decomposition products each has a characteristic reducing power of its own and, therefore, the reducing power of the mixed solution represents the. resultant of that of all the substances present and cannotbe used as a measure of the concentration of any single one of the products present. It is, therefore, exceedingly difiicult to determine just when the concentration of fructose in the mixed solution has reached a maximum value.

It has nowbeen found that as the hydrolysis of inulin progresses, the value of'the negative rotation of polarized light, pro duced by the solution, usualy increases at the be 'nning of the hydrolysis and then later ecreases. Hitherto this first maximum negative value of rotation has frequently been taken to indicate the highest obtainable concentration of'fructose in the solution. I have discovered, however, that this is not the case and that if the hydrolysis be continued after the first maximum negative rotation is reached, the negative till no of the rotation again usually increases and passes through a second maxlmum. Similarly several diderent maximum values .of negative rotation may be passed through during the course of the hydrolysis before' thehighest-possible negative rotation. is attained. Furthermore, I have found that when the hydrolysis is carried out in accordance with the method of the present inven tion, this final maximum or highest attainablenegative rotation, corres onds very closely to the maximum theoretical rotation of the solution, calculated uponthe basis that all of the inulin present in the solution is converted entirely into fructose. Fructose exists in two tautomeric. forms which are probably stereoisomers, and are supposed to have the following formulaeonion on on 011,011

. I 0 o HO-ti-H H0i-H n- '-on .H' --on n t l H i l draon dmon will be referred to in the claims as the maximum negative rotation. In this calculation the specific rotation [d1 of fructose is taken as minus ninety three degrees and the concentration of inulin in the solution is calculated from the weight of purified inulin dried to constant weight at 90 0., which was originally employed in making up the solution. in this calculation the formula of inulin dried under these conditions is taken as C H O The foregoing methods furnish criteria for judging the extent of the hydrolysis of inulin to fructose and therefore furnish means of'determining the total amount of impurities present in any .given instance under the particular conditions of hydrolysis employed. The total amount of these impuritics corresponds to the difference between the percentage of inulin which 18 completely hydrolyzed to fructose and one hundred percent. T have found that these 1mpurities are objectionable because they interfare with the subsequent crystallization of proximately fructose from solution and also because they impart increased hygrosco ic properties to. the solid fructose obtaine by crystallization or by evaporation of the hydrolized solution completelyto dryness, in accordance with methods such as that described in my co-pending application, Serial No. 369,537. Moreover, in many, instances certain of these im urities, particularly those formed by the ecomposition of fructose after the later has been formed, produce objectionable discoloration of the solution and also discolor the solid fructose obtained therefrom. They also impart a variable or objectionable flavor to the product.

Also I have found that there is an optimum concentration for any given acid, by means of which substantially one hundred percent conversion of inulin to fructose can be obtained. A greater or smaller concentration than this optimum concentration gives a poorer result. It has now been found that to obtain a maximum conversion with astrong inorganic acid requires a greater optiinum concentration of-acid than with an organic acid. Thus, for exam le, theopti mum concentration for hydroc loric' acid is approximately five hundredths 'normal, while with acetic acid the optimum-concentration is only about six thousandths normal. With hydrochloric acid of this optimum concentration, the maximum conver-- sion of inulin to fructose is reached in about five to ten minutes, whereas with acetic acid, of the above given optimum concentration, eight hours are-required to produce a maximum conversion of the inulin to fructose. In general I prefer to use organic acidsin concentration of from 0.005 to 0.01.5 normal.

Furthermore, I have discovered that the time re uiredto reach a maximum -conver- .sion wit i any given acid bears a certain definite and fixed relation to the concentration of the acid and that for each kind of acid, keeping the inulin concentration constant, this optimum time required for maximum conversion increases as theconcentration of llltll the acid diminishes, in such a way that the logarithm of the reciprocal of the time is aplproportional to. the logarithm of the norma concentration of the acid. In other words, the acid strength plotted against the reciprocal of the corresponding time gives an approximate} straight line on logarithmic paper. A terent line is ob-- tained, of course, for each kind of acid. Furthermore, I have discovered that the results obtained with certain organic acidssuch as acetic, citric, maleic, malic, fumaric lactic and tartaric acid and the like when plotted in this manner, give straight lines which are approximatel parallel and which lie relatively close toget \er. in other words,

I have discovered that'for diderent acids belonging tothis general-class, approximately Leg. N=ajlog. %+io b.

In which fibl represents the'normality of the acid in the usual sense, assuming that only the first hydrogen ion of the acid is active, while T is the time required for the highest possible yield, expresmd in hours and in which the constant a has a value between about .7 and 1. and the constant 6 has a value varying between about .007 5 and .03. The foregoing relationship between concentration and time holds good for temperatures between about C. and 120 C. and for pressures 'of about one atmosphere. This relationship is not seriously affected by changes in the original concentration of the inulih solution for concentrations greater, than about eight per cent by weight.

While it is desired that the scope of the present invention shall not be restricted by any unproven assumptions as to the exact chemical nature or the reactions produced during the hydrolysis, by certain organic acids such as acetic, citric, maleic, malic, fumaric, lactic and tartaric acids on the one hand and by inorganic acids such'as hydro-- chloric acid on the other hand, nevertheless,

it'is believed that the wide difference in their act-ion may be best er iplained in the following manner. The acid, it is thought, acts as a catalyst in the hydrolysis of inuhn by "virtue of the hydrogen ion concentration, while the failure of any given acid to produce a one hundred per cent conversion under certain conditions or with certain concentrations is believed to be due to a condensing action of the nndissociated molecules of the acid or of theaction upon the roducts of the hydrolysis of inulin and particularly upon the fructose. In other words, at each stage of the hydrolysis there seems to be two reactions going on which are opposed to each other in their effects, one reaction producing hydrolysis of inulin, probabl through several intermediate'stagcs, an another reaction bringing about decomposition or a condensation of the different hydrolytic products and particularly of fructose.

I believe that there are three principal stages in the hydrolysisof inulin and that two principal intermediate hydrolytic products are formed. before fructose is produced, thus lnulinficompound #1- compound #2'- fructose.

The reason, accordiug:,to my belief, that thefin'al stage has never hitherto been completely attained, is that the hydrolysis has been. conducted under-such conditions that the acid destroys the fructose or the intermediate compounds forming hygroscopic subto stances such as levulosin, and also other decomposition products such as humin, levu- 'linic acid, formic acid, etc. It is my belief also that the several diderent maxima of polarization already described, which are obtained during the course of the hydrolysis, correspond to maximum concentrations of these principal'intermediate hydrolytic compounds and I am convinced that this is the reason that the significance of these different maxima has hitherto been misunderstood resulting in a failure to obtain pure fructose directly from inulin as in the improved method of the present invention.

An example ofmy preferred method of 35 I carrying out the hydrolysis of inulin prepared and purified in accordance with the -methods described in my copending application,'Serial Number 424,459, is as follows:

'Damp cakes of inulin containing approximately 33 7 inulin are stirred up thoroughly with a small amount of a solution containing tartaric acid in an amount necessary to make the'solution .005 N-when the cakes have been liquefied by h drolysis and assuming that the tartaric aci functions as .a mono-basic acid, only the first'H ion being active. Specifically, I may take kilograms of inulin cake obtained by filter pressing or otherwise, containing 30-60% anhydrous inulin as determined by drying to constant weight at 90 C. This is put into an acid-proof vessel provided with an agitator and means for heating and is heated to 100 C. with continuous stirring, where-' upon it assumes a thin creamy consistency. Tartaric'acid, 75 gms. dissolved in a small amount of water, say one litre, is now added and the heating continued for between two and three hours, or until approximately 100%of the inulin has been converted into fructose as determined by polariscopic tests as previously described. The resulting product is a practically pure concentrated s rupy solution ofv fructose. I A smaller or. arger amount of tartaric acid can be used with a corresponding change in the'time as previously specified. The syrup may be used as suc 1 or evaporated or crystallized as for example as described in my co-pending applications Serial No. 309,537 and Serial No. 424,459,

It will be understood that I do not rcstrict myself to the particular proportions and conditions described in the preceding example, but I may alter or vary these in accordance with the general characteristics and features of my invention as previously described.

Among the principal advantages of the improved fructose food-product of the present invention, as compared with similar products hitherto known, are its greater stability especially toward heat, its exceptionally good keeping qualities, and in solid or crystalline form its greater freedom from a tendency to cake or become pasty when exposed to a moist or humid atmosphere. These special advantages of the new product particularly its greater stability toward heat and its improved keeping qualities are due in large part, I believe, to the unusual purity of the product and to the nature and degree of its acidity. In some instances (and particularly where good keeping qualities are especially desired) 1 have found that these advantageous properties can be increased by first l'iydrolyzing the pure inulin with the limited amount of acid as specified and then, after the hydrolysis is completed and the product has cooled, adding an additional amount of acid either to the syrup or to the solid or crystalline product obtained therefrom by evaporation or crystallization as, for example, by the method of evaporation and crystallization described in my co-pendmg applications. Serial No. 369,537 and Serial No. 424,459. Where the product is intended for consumption as a food itself or as a constituent of a food, ll prefer to add an innocuous or edible acid such as citric acid and preferably-tartaric acid or an acid tartrate or the like.

In the manufacture of candy or confectionery andin many culinary operations where a sugar is employed. it is highly desirable that the sugar shall not decompose or darken in color when cooked or heated and the improved pure fructose foodprodnet of the present invention meets these requirements in a much more satisfactory manner than any similar product hitherto known.

When a pure fructose syrup, prepared according to my invention, is allowed to stand for several days, it sometimes becomes slightly cloudy. which is objectionable, and T have found that this cloudiness is due to the formation of a small amount of calcium tartrate. The calcium comes from minute traces of compounds of this metal which sometimes remain in the clarified inulin-containing juices after clarification, unless special care is taken to remove these last traces of calcium in some convenient manner. lif

tartaric acid is used for hydrolysis this difliculty can be overcome by filtering the syrup before bottling it, after it has been stored for a few days. A still better method of avoiding this difficulty is to carry out the hydrolysis by means of an organic acid which forms calcium salt more soluble than calcium tartrate, such as lactic, maleic, malic, or fumaric acid.

This application is a division of my prior application Serial No. 484,153, filed July 12, 1921.

I claim:

1. The method-of preparing concentrated fructose syrup which comprises subjecting purified inulin to the action of less than about 7 0% of water and an amount of organic acid suflicient to produce a concentration of hydrogen ion of from about five hundredths to about fifteen thousandths normal in the mixture of inulin and Water in a liquefied state and then heating the acidified mixture thus obtained to convert the inulin to fructose.

2. The method of preparing concentrated fructose syrup which comprises subjecting purified inulin to the action of less than about of water and an amount of organic acid sufiicient to produce a concentration of hydrogen ion of from about five hundredths to about fifteen thousandths normal in the mixture of inulin and water in a liquefied state and. then heating the acidified mixture thus obtained until the inulin is substantially completely converted into fructose in concentrated solution and then separatingthe fructose from the solution in solid form.

3. The method of preparing concentrated fructose syrup which comprises subjecting purified inulin to the action of less than about 70% of water and an amount of organic acid sufficient to produce a concentra tion of hydrogen ion of from about five hundrcdths to fifteen thousandths normal in the mixture of inulin and water in a liquefied state and then heating the acidified mixture thus obtained until the inulin is substantially completely converted into fructose in concentrat-ed solution and then separating the fructose from the solution by crystallization.

In testimony whereof I afix my signature WILLIAM G. ARSEM. 

